1. Field of the Invention
This invention relates to an improved apparatus for forming CO.sub.2 snow within a freight container. The instant apparatus is more efficient than the apparatus disclosed in my prior U.S. Pat. No. 4,640,460, dated Feb. 3, 1987 in that the liquid CO.sub.2 discharged from nozzles supported from header lines or pipes is supplied to the latter through a supply pipe onto which CO.sub.2 snow discharged from the nozzles is impacted and the ends of the header pipes, from which the nozzles are supported, remote from the inlet ends thereof receiving liquid CO.sub.2 from the supply pipe open into the inlet or upstream end of the supply pipe in a manner functioning as an eductor such that the rapid inflow of liquid CO.sub.2 past the downstream ends of the header pipes creates a partial vacuum therein to recirculate some of the liquid CO.sub.2 from the downstream ends of the header pipes into the upstream or inlet end of the supply pipe.
The recirculating liquid CO.sub.2 has been previously chilled by the CO.sub.2 snow impacting with the exterior of the supply pipe and thus the liquid CO.sub.2 passing through the supply pipe to the header pipes is repeatedly lowered in temperature (from approximately 0.degree. F. at 300 psig) to closely approach the triple point temperature (approximately -69.degree. F. at 75 lbs. per sq. inch absolute). Thus, after several minutes of initial charging of a box car volume container (which process takes about 1 1/2 to 2 hours) the temperature of the liquid CO.sub.2 being discharged from the snow forming nozzles or heads approaches the triple point temperature and the CO.sub.2 snow forming operation is therefore carried at maximum efficiency.
2. Description of Related Art
My prior U.S. Pat. No. 4,640,460 discloses the concept of discharging CO.sub.2 snow directly upon opposite sides of a supply pipe through which liquid CO.sub.2 under pressure flows toward header pipes from which snow forming headers or nozzles are mounted. However, U.S. Pat. No. 4,640,460 does not disclose the concept of recirculating a portion of the liquid CO.sub.2 entering the supply pipe and thus the liquid CO.sub.2 being discharged from the nozzles or heads is only once cooled prior to being discharged from the nozzles or heads and not accumulatively cooled as is accomplished by the recirculation feature of the instant invention.